1. Field of the Invention
The invention relates to a network system, a method, and a network node by which a push-to talk function is realised.
2. Description of the Related Art
The invention relates to Push-To-Talk over Cellular (PoC). PoC is an open standard for PTT (Push-To-Talk) “walkie-talkie” technology. Created by the OMA (Open Mobile Alliance) standards organization, PoC uses VoIP (Voice over Internet Protocol) technology to stream voice over data networks such as GPRS (General Packet Radio Service).
In particular, PoC provides a connection of a network node (such as a mobile phone) to other network nodes. That is, a user starts a call with a push of key, similar as in “walkie-talkies”. Push to talk calls are one-way communications, while one person speaks, the other(s) listen. A push-to talk connection is typically connected virtually instantaneously, that is, an “always-on” and bursty connection is provided.
As mentioned above, PoC uses the existing technology of the GPRS networks. That is, the connection is provided via the GPRS network control nodes such as SGSN (Serving GPRS Support Node) and GGSN (Gateway GPRS Support Node) and the like. Furthermore, for the PoC functionality, an additional PoC application server is provided, which is responsible for the basic PoC functions, group management, floor control, distribution and filtering of voice messages and the like.
That is, PoC involves considerable signalling in the network, since PoC is provided via the normal network resources such as base stations and the like. It can be expected that the PoC service will be used very frequently. Hence, the load on the current networks will raise very high, which might lead to the problem that—due to limited network sources—the service cannot be provided properly and cost-effectively.